Spellchecking the preëdit should only spellcheck the part of the preedit which is a word

[mike-fabian]

https://user-images.githubusercontent.com/2330175/130404906-534222d9-ee14-4ff5-82e4-654d88d6b111.mp4

[mike-fabian]

The video shows that special characters like an opening parentheses are included in the spellchecking of the preëdit and make the spellchecking needlessly indicate an error:

• “test” is shown in black because it is a valid English word.
• “testi” and “testin” are shown in red because the spellchecker says they are not valid English words
• “testing” is shown in black again as it is a valid English word
• “(test”, “(testing” are shown in red even though the words alone without the opening parentheses would have been valid English words.

[mike-fabian]

Improved behaviour:

https://user-images.githubusercontent.com/2330175/130477103-6959234d-cf31-4eb5-b828-a2db3828906c.mp4